High speed!
This means that the signal of 145MHz(145M signal cycles per second) can be effectively amplified.
To be understood in connection with the following, there is a very important indicator called GBW(Gain Band Width).
It is the product of Gain and Bandwidth, called gain bandwidth product, GBW=Gain*Bandwidth;
He said that -3dB is the maximum GBW, that is, if your gain is 1, then the maximum signal frequency that can be effectively amplified is 145MHz; If the gain is 2, then the frequency of the best effectively amplified signal is 145\/2(MHz);
And then, you'll do the math, you see.